1. Field of the invention
This invention relates generally to earth and material handling equipment. More particularly, it relates to an improved apparatus for providing padding material during the installation of an underground pipeline or other conduit, including creating bottom pads, or bench pads, from the excavated material that results from digging a trench or other cavity.
2. Description of the related art
Underground pipelines are typically used to transport matter from one location to another. Such piping is commonly coated with plastic or an equivalent protective substance to prevent it from corroding while it is in the ground. It is necessary that the piping be buried in such a way as not to dent or damage the pipe and especially the protective coating. This is typically done by placing a layer of fine soil or sand, commonly called padding material, immediately adjacent the exterior surface of the pipe prior to covering the pipe line trench with material previously excavated from the trench. This excavated material typically contains rocks which can damage the pipe if placed directly in contact with the pipe surface.
To lay such pipe, a ditch digger, backhoe or the like is used to dig an open trench. The excavated rocks and soil, often referred to as spoil or backfill, is typically piled to one side of the excavation forming a continuous mound running parallel to the trench. Before the pipe is placed in the trench, it is customary that a series of small bottom pads composed of padding material be spaced along the bottom of the trench. The pipe is then placed upon these pads and supported above the trench bottom at spaced intervals. This enables additional padding material to be placed completely around and under the pipe after the pipe is placed in the trench. Historically, the bottom pads, or bench pads, are typically done by hand. This entails a labor intensive process that can not only be expensive and time consuming but can be a substantial safety hazard for workers standing in the ditch since the ditch can be several feet deep and subject to collapse in certain soil conditions.
Once the pipe is placed in the trench and supported by the spaced bench pads, a pipeline padding machine, such as that disclosed in U.S. Pat. No. 5,084,991, may then be driven longitudinally along the side of the trench through the spoil to collect and process the excavated material to partially fill the trench with fine padding material that is separated out of the excavated spoil. It is preferred to extract the fine material out of the spoil so that the remaining coarse particles in the spoil do not come into direct contact with the pipe surface, which can damage the coating and cause undesirable damage or corrosion of the pipeline.
U.S. Pat. No. 2,857,691, which issued Oct. 28, 1958 to Donald Michael Curran, and is entitled "Pipeline Ditch Filling and Pipe Padding Machine," is directed to obtaining and depositing padding material from the spoil to the trench. This patent discloses the use of a rotating head to collect and elevate excavated material and extract fine material (i.e. fines) from the spoil and a conveyor to carry the fines to the trench. However, Curran discloses an arm which extends across the ditch and is moved longitudinally through the spoil along the side of the trench and elevates excavated material and extracts some of the material as the entire device moves along the trench to provide a continuous supply of padding material. As a result, such devices have been found to be very difficult to control and operate due to the lateral torque placed upon the extended arm and the tractor. Also, the continuous nature of the device makes the formation of a single bench pad somewhat difficult and would possibly require that the device be forced through the spoil twice--once to form bench pads and a second time to provide additional padding material around the pipe. The additional stress on these devices tends to reduce the duration for which they can be utilized. A shorter life span of such padding devices also makes the process of constructing bench pads expensive.
In addition to a need for a more economical process of constructing bench pads, there is a need for a padder that is adaptable to various types of terrain, especially in places that are difficult for existing padding machines to access.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.